The present invention relates generally to microwave diplexers, and more particularly to microwave diplexers employing complementary filtering techniques.
Diplexers are commonly known in the communications art, and are generally employed where several distinct frequencies are transmitted or received over the same communications link. For example, satellite communications systems employ microwave communication systems which commonly use diplexers to control the movement of separately distinct transmit and receive frequencies through the communication system. A diplexer is generally required to connect circuits which exclusively operate at one of the two frequencies to circuits which may utilize both frequencies.
In order to accomplish the diplexing function, prior diplexing schemes have utilized a waveguide cavity transmission filter tuned to one frequency coupled to a waveguide tuned to the second frequency but having a frequency cut off at the first frequency. Both the transmission filter and the waveguide are tapped into a second waveguide which is suitable for transmitting both frequencies.
Another prior art diplexer is disclosed in a publication entitled "Printed-Circuit Complementary Filters for Narrow Bandwidth Multiplexers", by Wenzel, in IEEE Transactions on Microwave Theory and Techniques, March 1968, pages 147 to 157. This publication generally discusses design techniques and interconnection equivalent circuits for constructing printed circuit narrowband complementary filters. The disclosed techniques describe contiguous band multiplexers using a single printed circuit board with no series or shorted stubs. Equivalent circuit transformations are discussed for design of a two-section stripline complementary filter pair.